Magnetic Characteristics of Praseodymium, Neodymium, and Samarium Hydrides

Abstract

Magnetization‐temperature data are presented for the hydrides PrH_2.02 to PrH_2.71, NdH_2.02 to NdH_2.75, and SmH_1.99 to SmH_2.88 and for the three parent metals from 4.2° to 300°K. Of the twelve hydrides examined only NdH_2.02 and NdH_2.03 exhibited magnetic ordering. These hydrides exhibited a Curie point at 9.5°K and the saturation moment measured at 4.2°K was 1.36 μ_B per Nd atom. Assuming the applicability of a Brillouin function with J=9/2 the moment extrapolated to 0°K is 1.51 μ_B. These values are considerably lower than the value for the free tripositive ion (3.27 μ_B) or the moment observed in the paramagnetic region (3.40 μ_B) but are in reasonably good agreement with the theoretical value (1.58 μ_B) computed for 4.2°K taking into account crystal field effects. The susceptibility behavior of the four Sm hydrides studied is generally similar. The trend with temperature is in reasonably good agreement with theory which treats Sm as a free tripositive ion. Susceptibility of the Nd hydrides follow the Curie‐Weiss law above about 100°K with the expected slope but deviate negatively from it at lower temperatures. The deviations are attributed to either incipient ferromagnetic ordering or crystal field effects or a combination of the two. The susceptibility behavior of the Pr hydrides is very unusual. The highest hydrides exhibit Curie‐Weiss behavior above about 80°K but show positive deviations from linearity in 1/χ vs T at lower temperatures. That the deviations may be due to crystal field effects is considered possible but unlikely. PrH_2.03 and PrH_2.04 exhibit essentially identical susceptibility behavior and do not follow the Curie‐Weiss law. Their susceptibilities are anomalously high near room temperature, exceeding the values for the element and the saturated hydride by a factor of about five.